Law Of Thermodynamics Quiz Questions

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  • 1/54 Questions

    Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?

    • Anabolism
    • Dehydration
    • Metabolism
    • Catabolism
    • Catalysis
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Thermodynamics Quizzes & Trivia
About This Quiz

There are four known laws of thermodynamics and the first one is the law of conservation of energy, which states that energy can neither be created nor destroyed. The quiz below covers how well you understand the different laws of thermodynamics and how to apply them in everyday life. All the best!

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  • 2. 

    Which of the following is (are) true for anabolic pathways?

    • They consume energy to build up polymers from monomers.

    • They do not depend on enzymes.

    • They are usually highly spontaneous chemical reactions.

    • They release energy as they degrade polymers to monomers.

    Correct Answer
    A. They consume energy to build up polymers from monomers.
    Explanation
    Anabolic pathways involve the synthesis of complex molecules from simpler ones, such as building polymers from monomers. This process requires energy input, usually in the form of ATP, to drive the chemical reactions. Enzymes are essential in anabolic pathways to catalyze and regulate the reactions, so the statement that anabolic pathways do not depend on enzymes is incorrect. The statement that anabolic pathways release energy as they degrade polymers to monomers is also incorrect, as this describes catabolic pathways. Anabolic reactions are typically not highly spontaneous, as they require an input of energy to proceed.

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  • 3. 

    Which of the following is a statement of the first law of thermodynamics?

    • Energy cannot be transferred or transformed.

    • The entropy of the universe is decreasing.

    • Kinetic energy is stored energy that results from the specific arrangement of matter.

    • The entropy of the universe is constant.

    • Energy cannot be created nor destroyed

    Correct Answer
    A. Energy cannot be created nor destroyed
    Explanation
    The first law of thermodynamics, also known as the law of conservation of energy, states that energy cannot be created nor destroyed, but it can only be transferred or transformed from one form to another. This means that the total amount of energy in a closed system remains constant.

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  • 4. 

    For living organisms, which of the following is an important consequence of the first law of thermodynamics?

    • The organism ultimately must obtain all of the necessary energy for life from its environment.

    • Organisms are unable to transform energy.

    • The entropy of an organism decreases with time as the organism grows in complexity.

    • The energy content of an organism is constant.

    • Life does not obey the first law of thermodynamics.

    Correct Answer
    A. The organism ultimately must obtain all of the necessary energy for life from its environment.
    Explanation
    The first law of thermodynamics states that energy cannot be created or destroyed, only transferred or transformed. This means that living organisms cannot create energy, but rather must obtain it from their environment. This is because energy is required for various life processes such as growth, reproduction, and metabolism. Therefore, the correct answer is that the organism ultimately must obtain all of the necessary energy for life from its environment.

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  • 5. 

    Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics?

    • Life obeys the second law of thermodynamics because the decrease in entropy as the

    • Living organisms are able to transform energy into entropy.

    • As a consequence of growing, organisms create more disorder in their environment than the

    • Living organisms do not obey the second law of thermodynamics, which states that entropy

    • Living organisms do not follow the laws of thermodynamics.

    Correct Answer
    A. As a consequence of growing, organisms create more disorder in their environment than the
  • 6. 

    Whenever energy is transformed, there is always an increase in the

    • Enthalpy of the universe

    • Free energy of the system

    • Free energy of the universe

    • Entropy of the universe

    • Entropy of the system

    Correct Answer
    A. Entropy of the universe
    Explanation
    Whenever energy is transformed, the overall entropy of the universe increases. This is because energy transformations tend to increase the disorder or randomness in the system, leading to an increase in entropy. The concept of entropy is closely related to the second law of thermodynamics, which states that the entropy of an isolated system always increases over time. Therefore, the correct answer is entropy of the universe.

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  • 7. 

    Which of the following statements is a logical consequence of the second law of thermodynamics?

    • Every chemical reaction must increase the total entropy of the universe.

    • If there is an increase in the energy of a system, there must be a corresponding decrease in the

    • Energy can be transferred or transformed, but it cannot be created or destroyed.

    • If the entropy of a system increases, there must be a corresponding decrease in the entropy of

    • Every energy transfer requires activation energy from the environment.

    Correct Answer
    A. Every chemical reaction must increase the total entropy of the universe.
    Explanation
    The second law of thermodynamics states that the entropy of an isolated system will always increase over time. Entropy can be thought of as a measure of the disorder or randomness in a system. Since chemical reactions involve the rearrangement of atoms and molecules, they can lead to an increase in the overall disorder of the system, resulting in an increase in entropy. Therefore, it is a logical consequence of the second law of thermodynamics that every chemical reaction must increase the total entropy of the universe.

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  • 8. 

    Which of the following statements is representative of the second law of thermodynamics?

    • Heat represents a form of energy that can be used by most organisms to do work.

    • Every energy transformation by a cell decreases the entropy of the universe.

    • Without an input of energy, organisms would tend toward decreasing entropy.

    • Cells require a constant input of energy to maintain their high level of organisation.

    • Conversion of energy from one form to another is always accompanied by some gain of free

    Correct Answer
    A. Cells require a constant input of energy to maintain their high level of organisation.
    Explanation
    The second law of thermodynamics states that the entropy of an isolated system always increases over time. This means that without an input of energy, the entropy of a system will tend to increase. In the context of the given options, the statement "Cells require a constant input of energy to maintain their high level of organization" is representative of the second law of thermodynamics because it implies that cells need energy to counteract the tendency towards increasing entropy and maintain their organized state.

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  • 9. 

    Which of the following types of reactions would decrease the entropy within a cell?

    • Hydrolysis

    • Respiration

    • Dehydation reaction

    • Catabolism

    • Digestion

    Correct Answer
    A. Dehydation reaction
    Explanation
    A dehydration reaction involves the removal of water molecules to form a larger molecule. This process leads to a decrease in the number of molecules within the cell, resulting in a decrease in entropy. Therefore, a dehydration reaction would decrease the entropy within a cell.

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  • 10. 

    The organisation of organisms has become increasingly complex with time. This statement

    • Requires that due to evolution, the entropy of the universe increased.

    • Is based on the fact that organisms function as closed systems.

    • Is consistent with the second law of thermodynamics.

    • A and B only

    • A, B and C

    Correct Answer
    A. Is consistent with the second law of thermodynamics.
    Explanation
    The statement suggests that the organization of organisms has become more complex over time, which aligns with the second law of thermodynamics. This law states that the entropy, or disorder, of a closed system tends to increase over time. As organisms are considered closed systems, their increasing complexity implies a decrease in entropy, which is consistent with the second law of thermodynamics.

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  • 11. 

    Which of the following is an example of potential rather than kinetic energy?

    • A firefly using light flashes to attract a mate

    • Boy mowing grass

    • A food molecule made up of energy-rich macromolecules

    • Water rushing over Niagara Falls

    • An insect foraging for food

    Correct Answer
    A. A food molecule made up of energy-rich macromolecules
    Explanation
    A food molecule made up of energy-rich macromolecules is an example of potential energy rather than kinetic energy. Potential energy refers to stored energy that has the potential to be converted into kinetic energy. In this case, the food molecule contains energy that can be released and converted into kinetic energy when it is metabolized by an organism. This potential energy is not currently being used or in motion, making it an example of potential energy.

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  • 12. 

    Which of the following is considered an open system?

    • A sealed terrarium

    • Food cooking in a pressure cooker

    • An organism

    • Liquid in a corked bottle

    Correct Answer
    A. An organism
    Explanation
    An organism is considered an open system because it interacts with its environment, exchanging matter and energy. It takes in nutrients, releases waste, and constantly adjusts its internal processes to maintain homeostasis. In contrast, a sealed terrarium, food cooking in a pressure cooker, and liquid in a corked bottle are all closed systems because they do not exchange matter or energy with their surroundings.

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  • 13. 

    Which of the following is true of metabolism in its entirety?

    • Metabolism is a property of organismal life

    • Metabolism depends on an organism's adequate hydration

    • Metabolism manages the increase of entropy in an organism

    • Metabolism utilises all of an organism's resources

    • Metabolism depends on a constant supply of energy from food

    Correct Answer
    A. Metabolism is a property of organismal life
    Explanation
    Metabolism is a property of organismal life means that metabolism is a characteristic or attribute that is unique to living organisms. It refers to the set of chemical reactions that occur within an organism to maintain life, including processes such as breaking down food for energy, synthesizing molecules, and eliminating waste. This statement implies that metabolism is a fundamental aspect of living organisms and is essential for their survival and functioning.

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  • 14. 

    Which of the following best describes the change in free energy in a system at chemical equilibrium?

    • Slightly decreasing

    • Greatly increasing

    • Slightly increasing

    • Greatly decreasing

    • No change

    Correct Answer
    A. No change
    Explanation
    At chemical equilibrium, the forward and reverse reactions occur at the same rate, resulting in a balance between the reactants and products. This means that the system has reached a state of minimum free energy, where there is no net change in the amount of reactants and products. Therefore, the correct answer is "No change."

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  • 15. 

    Which of the following is true for all exergonic reactions?

    • The reaction proceeds with a net release of free energy.

    • The products have more total energy than the reactants.

    • Some reactants will be converted to products.

    • The reactions are nonspontaneous.

    • A net input of energy from the surroundings is required for the reactions to proceed.

    Correct Answer
    A. The reaction proceeds with a net release of free energy.
    Explanation
    Exergonic reactions are characterized by a net release of free energy. This means that the products of the reaction have less energy than the reactants, resulting in a spontaneous release of energy. In other words, exergonic reactions release energy as they proceed, making them favorable and spontaneous. This is in contrast to endergonic reactions, which require an input of energy to proceed. Therefore, the statement "The reaction proceeds with a net release of free energy" accurately describes all exergonic reactions.

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  • 16. 

    Chemical equilibrium is relatively rare in living cells. Which of the following could be an example of a reaction at chemical equilibrium in a cell?

    • A chemical reaction in which the entropy change in the reaction is just balanced by an

    • A reaction in which the free energy at equilibrium is higher than the energy content at any

    • An endergonic reaction in an active metabolic pathway where the energy for that reaction is

    • A chemical reaction in which both the reactants and products are only used in a metabolic

    • There is no possibility of having chemical equilibrium in any living cell.

    Correct Answer
    A. A chemical reaction in which both the reactants and products are only used in a metabolic
  • 17. 

    A chemical reaction that has a positive 􀁐G is correctly described as

    • Endothermic

    • Enthalpic

    • Spontaneous

    • Endergonic

    • Exothermic

    Correct Answer
    A. Endergonic
    Explanation
    A chemical reaction that has a positive ΔG is correctly described as endergonic. Endergonic reactions require an input of energy in order to proceed, meaning that the products have more free energy than the reactants. This is opposite to exergonic reactions, which release energy and have a negative ΔG. Therefore, endergonic reactions are not spontaneous and require an input of energy to occur.

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  • 18. 

    Which of the following best describes enthalpy (H)?

    • The system's entropy

    • The condition of a cell that is not able to react

    • The cell's energy equilibrium

    • The heat content of a chemical system

    • The total kinetic energy of a system

    Correct Answer
    A. The heat content of a chemical system
    Explanation
    Enthalpy (H) is a thermodynamic property that represents the heat content of a chemical system. It includes both the internal energy of the system and the work done by or on the system. It is a measure of the total energy of the system and is often used in chemical reactions to determine the heat exchange with the surroundings. Therefore, the correct answer is "the heat content of a chemical system".

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  • 19. 

    Why is ATP an important molecule in metabolism?

    • It provides energy coupling between exergonic and endergonic reactions.

    • Its terminal phosphate group contains a strong covalent bond that when hydrolysed releases

    • Its terminal phosphate bond has higher energy than the other two.

    • Its hydrolysis provides an input of free energy for exergonic reactions.

    • All of the above are true.

    Correct Answer
    A. It provides energy coupling between exergonic and endergonic reactions.
    Explanation
    ATP is an important molecule in metabolism because it provides energy coupling between exergonic and endergonic reactions. This means that it can transfer energy from reactions that release energy (exergonic) to reactions that require energy (endergonic). ATP achieves this through the hydrolysis of its terminal phosphate bond, which releases energy that can be used to drive other reactions. Therefore, all of the given statements are true and contribute to the importance of ATP in metabolism.

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  • 20. 

    When 10,000 molecules of ATP are hydrolyxed to ADP and Pi in a test tube, about twice as much heat is liberated as when a cell hydrolyses the same amount of ATP. Which of the following is the best explanation for this observation?

    • Reactant and product concentrations are not the same

    • Cells are open systems, but a test tube is a closed system.

    • The hydrolysis of ATP in a cell produces different chemical products than does the reaction in

    • The reaction in cells must be catalysed by enzymes, but the reaction in a test tube does not

    • Cells are less efficient at heat production than nonliving systems.

    Correct Answer
    A. Reactant and product concentrations are not the same
    Explanation
    The best explanation for the observation that more heat is liberated when 10,000 molecules of ATP are hydrolyzed in a test tube compared to a cell is that the reactant and product concentrations are not the same. This means that the concentration of ATP and its products, ADP and Pi, are different in the test tube compared to the cell. This difference in concentrations can affect the amount of heat released during the hydrolysis reaction.

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  • 21. 

    Which of the following is most similar in structure to ATP?

    • A phosophilip

    • An RNA nucleotide

    • An amino acid with three phosphate groups

    • A DNA helix

    • An anabolic steroid

    Correct Answer
    A. An RNA nucleotide
    Explanation
    An RNA nucleotide is most similar in structure to ATP because both molecules contain a sugar (ribose in RNA nucleotide and ribose or deoxyribose in ATP), a nitrogenous base (adenine in both cases), and phosphate groups. Both ATP and RNA nucleotides are involved in energy transfer and storage in cells.

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  • 22. 

    What term is used to describe the transfer of free energy from catabolic pathways to anabolic pathways?

    • Feedback regulation

    • Entropy

    • Bioenergetics

    • Cooperativity

    • Energy coupling

    Correct Answer
    A. Energy coupling
    Explanation
    Energy coupling is the term used to describe the transfer of free energy from catabolic pathways to anabolic pathways. This process involves the use of ATP, which is produced during catabolism and then used as a source of energy for anabolism. Energy coupling allows for the efficient transfer and utilization of energy within the cell, ensuring that the energy released from catabolic reactions is harnessed and used to drive anabolic reactions.

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  • 23. 

    Which of the following statements is true concerning catabolic pathways?

    • They build up complex molecules such as protein from simpler compounds.

    • They combine molecules into more energy-rich molecules.

    • They are usually coupled with anabolic pathways to which they supply energy in the form of

    • They are endergonic.

    • They are spontaneous and do not need enzyme catalysis.

    Correct Answer
    A. They are usually coupled with anabolic pathways to which they supply energy in the form of
  • 24. 

    When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?

    • It is lost to the environment.

    • It is used to generate ADP from nucleotide precursors.

    • It is used to store energy as more ATP.

    • It is transported to specific organs such as the brain.

    • It is used to power yet more cellular work.

    Correct Answer
    A. It is lost to the environment.
    Explanation
    When chemical, transport, or mechanical work is done by an organism, the heat generated is lost to the environment. This means that the heat is dissipated into the surrounding environment and does not contribute to any further energy storage or use within the organism.

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  • 25. 

    When ATP releases some energy, it also releases inorganic phosphate. What purpose does this serve (if any) in the cell?

    • It can be added to water and excreted as a liquid.

    • It can only be used to regenerate more ATP.

    • It can enter the nucleus to affect gene expression.

    • It can be added to other molecules in order to activate them.

    • It is released as an excretory waste.

    Correct Answer
    A. It can be added to other molecules in order to activate them.
    Explanation
    When ATP releases inorganic phosphate, it can be added to other molecules in order to activate them. Inorganic phosphate can act as a phosphate group donor, which is necessary for many cellular processes. It can be added to molecules like proteins, enzymes, or other nucleotides to modify their structure or function. This phosphorylation process plays a crucial role in signal transduction, energy transfer, and regulation of cellular activities. Therefore, the release of inorganic phosphate by ATP serves the purpose of activating other molecules in the cell.

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  • 26. 

    What must be the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in DNA and RNA?

    • The nitrogen-containing base is different.

    • The number of phosphates is three instead of one.

    • The number of phosphates is three instead of two.

    • The sugar molecule is different.

    • There is no difference.

    Correct Answer
    A. There is no difference.
    Explanation
    The correct answer is that there is no difference between the structure of ATP and the precursor of the A nucleotide in DNA and RNA. This means that the nitrogen-containing base, the number of phosphates, and the sugar molecule are all the same in both ATP and the precursor of the A nucleotide.

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  • 27. 

    Which of the following statements is (are) true about enzyme-catalysed reactions?

    • The reaction always goes in the direction toward chemical equilibrium.

    • The reaction is faster than the same reaction in the absence of the enzyme.

    • The free energy change of the reaction is opposite from the reaction in the absence of the

    • A and B only

    • A, B and C

    Correct Answer
    A. The reaction is faster than the same reaction in the absence of the enzyme.
    Explanation
    Enzymes are biological catalysts that increase the rate of a chemical reaction. They do this by lowering the activation energy required for the reaction to occur. Therefore, the statement "The reaction is faster than the same reaction in the absence of the enzyme" is true. Enzymes do not affect the direction of the reaction or the free energy change, so the other statements are not true.

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  • 28. 

    How can one increase the rate of a chemical reaction?

    • Increase the entropy of the reactants.

    • Decrease the concentration of the reactants.

    • Cool the reactants.

    • Add a catalyst.

    • Increase the activation energy needed.

    Correct Answer
    A. Add a catalyst.
    Explanation
    Adding a catalyst can increase the rate of a chemical reaction by providing an alternative reaction pathway with lower activation energy. This lowers the energy barrier for the reaction to occur, allowing more reactant molecules to successfully collide and form products in a shorter amount of time. The catalyst itself is not consumed in the reaction and can be used repeatedly, making it an efficient way to increase the reaction rate.

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  • 29. 

    Sucrose is a disaccharide, composed of the monosaccharides glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase results in

    • Bringing glucose and fructose together to form sucrose.

    • Utilisation of water as a covalent bond is formed between glucose and fructose to form

    • Breaking the bond between glucose and fructose and forming new bonds from the atoms of

    • Production of water from the sugar as bonds are broken between the glucose monomers.

    • The release of water from sucrose as the bond between glucose and fructose is broken.

    Correct Answer
    A. Breaking the bond between glucose and fructose and forming new bonds from the atoms of
    Explanation
    The correct answer is "breaking the bond between glucose and fructose and forming new bonds from the atoms of". This is because hydrolysis is a chemical reaction that involves the breaking of a bond by the addition of water. In the case of sucrose, the bond between glucose and fructose is broken, and new bonds are formed from the atoms of glucose and fructose. This process results in the breakdown of sucrose into its individual monosaccharide components, glucose and fructose.

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  • 30. 

    Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's 

    • Entropy

    • Activation energy

    • Endothermic level

    • Free-energy content

    • Heat content

    Correct Answer
    A. Activation energy
    Explanation
    In order for reactants to form products in a chemical reaction, they must first overcome a thermodynamic barrier known as the reaction's activation energy. This is the minimum amount of energy required for the reaction to occur and for the reactant molecules to reach a transition state where new bonds can form and products can be produced. Without overcoming this barrier, the reaction will not proceed.

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  • 31. 

    A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because

    • The hydrolysis of starch to sugar is endergonic.

    • The activation energy barrier for this reaction cannot be surmounted.

    • Starch cannot be hydrolysed in the presence of so much water.

    • Starch hydrolysis is nonspontaneous.

    • The starch solution has less free energy than the sugar solution.

    Correct Answer
    A. The activation energy barrier for this reaction cannot be surmounted.
    Explanation
    The activation energy barrier refers to the energy required for a reaction to occur. In this case, the hydrolysis of starch to sugar requires breaking the bonds in starch molecules, which is a complex process. The activation energy barrier for this reaction is high, meaning that a significant amount of energy is needed to initiate the reaction. Therefore, at room temperature, the reaction does not occur readily because the activation energy barrier cannot be surmounted.

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  • 32. 

    Which of the following statements regarding enzymes is true?

    • Enzymes are permanently altered by the reactions they catalyse.

    • Enzymes prevent changes in substrate concentrations.

    • Enzymes increase the rate of a reaction.

    • Enzymes change the direction of chemical reactions.

    • Enzymes decrease the free energy change of a reaction.

    Correct Answer
    A. Enzymes increase the rate of a reaction.
    Explanation
    Enzymes increase the rate of a reaction by lowering the activation energy required for the reaction to occur. They do this by providing an alternative pathway for the reaction with a lower activation energy, allowing the reaction to proceed more quickly. This is possible because enzymes have a specific three-dimensional shape that allows them to bind to the reactant molecules, called substrates, and facilitate the conversion of substrates into products. This catalytic activity of enzymes makes them crucial for the efficient functioning of biological processes.

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  • 33. 

    During a laboratory experiment, you discover that an enzyme-catalysed reaction has a 􀁐G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the 􀁐G for the new reaction?

    • +40 kcal/mol

    • -20 kcal/mol

    • +20 kcal/mol

    • 0 kcal/mol

    • -40 kcal/mol

    Correct Answer
    A. -20 kcal/mol
    Explanation
    When the amount of enzyme in the reaction is doubled, it does not affect the 􀁐G value. Therefore, the 􀁐G for the new reaction will still be -20 kcal/mol.

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  • 34. 

    The active site of an enzyme is the region that

    • Binds allosteric regulators of the enzyme.

    • Is inhibited by the presence of a coenzyme or a cofactor.

    • Is involved in the catalytic reaction of the enzyme.

    • Binds the products of the catalytic reaction.

    Correct Answer
    A. Is involved in the catalytic reaction of the enzyme.
    Explanation
    The active site of an enzyme is the region that is involved in the catalytic reaction of the enzyme. This means that it is the specific location where the enzyme binds to its substrate and facilitates the chemical reaction to occur. The active site provides a complementary shape and chemical environment for the substrate to bind and undergo the reaction, leading to the formation of products. The binding of the substrate to the active site is highly specific and allows for the enzyme to catalyze the reaction efficiently.

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  • 35. 

    According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?

    • The binding of the substrate changes the shape of the enzyme's active site.

    • A competitive inhibitor can outcompete the substrate for the active site.

    • The active site creates a microenvironment ideal for the reaction.

    • The binding of the substrate depends on the shape of the active site.

    • Some enzymes change their structure when activators bind to the enzyme.

    Correct Answer
    A. The binding of the substrate changes the shape of the enzyme's active site.
    Explanation
    According to the induced fit hypothesis of enzyme catalysis, the correct statement is that the binding of the substrate changes the shape of the enzyme's active site. This means that the active site is not a rigid structure, but rather it can undergo conformational changes upon substrate binding. These changes in shape allow the enzyme to better accommodate and interact with the substrate, leading to catalysis of the reaction. This hypothesis suggests that the enzyme and substrate undergo a dynamic interaction, with the enzyme adapting its shape to fit the substrate.

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  • 36. 

    Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?

    • Competitive inhibition

    • Denaturisation of the enzyme

    • Allosteric inhibition

    • Insufficient cofactors

    • Saturation of the enzyme activity

    Correct Answer
    A. Competitive inhibition
    Explanation
    Increasing the substrate concentration in an enzymatic reaction could overcome competitive inhibition. Competitive inhibition occurs when a molecule similar to the substrate competes with the substrate for the active site of the enzyme. By increasing the substrate concentration, the chances of the substrate binding to the active site increase, reducing the likelihood of the inhibitor molecule binding. This allows more substrate molecules to bind and continue the enzymatic reaction, overcoming the inhibitory effect of the competitive inhibitor.

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  • 37. 

    Which of the following is true of enzymes?

    • Enzyme function is increased if the three-dimensional structure or conformation of an

    • Enzymes may require a nonprotein cofactor or ion for catalysis to take speed up more

    • Enzymes increase the rate of chemical reaction by lowering activation energy barriers.

    • Enzyme function is independent of physical and chemical environmental factors such as pH

    Correct Answer
    A. Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
    Explanation
    Enzymes increase the rate of chemical reaction by lowering activation energy barriers. Enzymes act as catalysts, facilitating chemical reactions by reducing the amount of energy needed for the reaction to occur. They achieve this by binding to the reactant molecules and bringing them into close proximity, allowing them to interact more easily and form products. This lowers the activation energy required for the reaction, making it more likely to occur and increasing the rate of the reaction. The other options are not true of enzymes as they do not accurately describe their function.

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  • 38. 

    Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as a(n)

    • Cofactor necessary for enzyme activity.

    • Competitive inhibitor of the enzyme.

    • Coenzyme derived from a vitamin.

    • Noncompetitive inhibitor of the enzyme.

    • Allosteric activator of the enzyme.

    Correct Answer
    A. Cofactor necessary for enzyme activity.
    Explanation
    Zinc is known to be an essential trace element for most organisms and is found in the active site of the enzyme carboxypeptidase. This suggests that zinc plays a crucial role in the functioning of the enzyme. In enzymes, a cofactor is a non-protein molecule or ion that is required for the enzyme to function properly. Therefore, the presence of zinc in the active site of carboxypeptidase indicates that it acts as a cofactor necessary for the enzyme's activity.

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  • 39. 

    Succinate dehydrogenase catalyses the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. Based on this information, which of the following is correct?

    • Succinate dehydrogenase is the enzyme, and malonic acid is the substrate.

    • Succinate is the substrate, and fumarate is the product.

    • Succinate dehydrogenase is the enzyme, and fumarate is the substrate.

    • Fumarate is the product, and malonic acid is a noncompetitive inhibitor.

    • Malonic acid is the product, and fumarate is a competitive inhibitor.

    Correct Answer
    A. Succinate is the substrate, and fumarate is the product.
    Explanation
    Succinate dehydrogenase is the enzyme responsible for catalyzing the conversion of succinate to fumarate. Therefore, succinate is the substrate, and fumarate is the product of this reaction.

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  • 40. 

    Succinate dehydrogenase catalyses the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. What is the purpose of using malonic acid in this experiment?

    • It replaces the usual enzyme.

    • It blocks the binding of fumarate.

    • It is a competitive inhibitor.

    • It is able to bind to succinate.

    • It is a noncompetitive inhibitor.

    Correct Answer
    A. It is a competitive inhibitor.
    Explanation
    Malonic acid is used in this experiment as a competitive inhibitor. Competitive inhibitors are molecules that resemble the substrate and compete with it for binding to the active site of the enzyme. In this case, malonic acid resembles succinate, the substrate of succinate dehydrogenase. By increasing the ratio of succinate to malonic acid, more succinate molecules are available to bind to the enzyme, reducing the inhibitory effect of malonic acid. This suggests that malonic acid competes with succinate for binding to the active site of succinate dehydrogenase, hence acting as a competitive inhibitor.

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  • 41. 

    In order to attach a particular amino acid to the tRNA molecule that will transport it, an enzyme, an aminoacyl-tRNA synthetase, is required, along with ATP. Initially, the enzyme has an active site for ATP and another for the amino acid, but it is not able to attach the tRNA. What must occur in order for the final attachment to occur?

    • The hydrolysis of the ATP must be needed to allow the amino acid to bind to the synthetase.

    • The 3' end of the tRNA must have to be cleaved before it can have an attached amino acid.

    • The ATP must first have to attach to the tRNA.

    • The binding of the first two molecules must cause a 3-dimensional change that opens another

    • The tRNA molecule must have to alter its shape in order to be able to fit into the active site

    Correct Answer
    A. The binding of the first two molecules must cause a 3-dimensional change that opens another
    Explanation
    The correct answer states that the binding of the ATP and the amino acid must cause a 3-dimensional change in the enzyme, which then opens another active site for the tRNA molecule to attach. This suggests that the enzyme undergoes a conformational change upon binding the ATP and the amino acid, allowing it to accommodate the tRNA molecule and facilitate the final attachment of the amino acid to the tRNA.

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  • 42. 

    Competitive inhibitors block the entry of substrate into the active site of an enzyme. On which of the following properties of an active site does this primarily depend?

    • The enzyme forming covalent bonds with the reactants

    • The enzyme's ability to stretch reactants and move them toward a transition state

    • The ability of an enzyme to form a template for holding and joining molecules

    • The enzyme providing an appropriate microenvironment conducive to a reaction's occurrence

    • The enzyme becoming too saturated because of the concentration of substrate

    Correct Answer
    A. The ability of an enzyme to form a template for holding and joining molecules
    Explanation
    Competitive inhibitors primarily depend on the ability of an enzyme to form a template for holding and joining molecules. This means that the active site of the enzyme has a specific shape and structure that allows it to bind to the substrate and facilitate the reaction. Competitive inhibitors can bind to the active site of the enzyme and prevent the substrate from binding, effectively blocking the entry of the substrate into the active site.

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  • 43. 

    Which of the following is likely to lead to an increase in the concentration of ATP in a cell?

    • An increase in a cell's catabolic activity

    • An increased amino acid concentration

    • An increased influx of cofactor molecules

    • The cell's increased transport of materials to the environment

    • An increase in a cell's anabolic activity

    Correct Answer
    A. An increase in a cell's catabolic activity
    Explanation
    An increase in a cell's catabolic activity is likely to lead to an increase in the concentration of ATP in a cell. Catabolic activity refers to the breakdown of complex molecules into simpler ones, releasing energy in the process. ATP is the primary energy currency in cells, and it is produced during cellular respiration, which is a catabolic process. Therefore, an increase in catabolic activity would result in more ATP being produced, leading to an increase in its concentration within the cell.

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  • 44. 

    When you have a severe fever, what may be a grave consequence if this is not controlled? 

    • Change in the folding of enzymes

    • Removal of amine groups from your proteins

    • Binding of enzymes to inappropriate substrates

    • Destruction of your enzymes' primary structure

    • Removal of the amino acids in active sites

    Correct Answer
    A. Change in the folding of enzymes
    Explanation
    If a severe fever is not controlled, it can lead to a change in the folding of enzymes. Enzymes are proteins that play a crucial role in various biological processes. They function properly when their structure is maintained. However, high body temperature can disrupt the normal folding of enzymes, causing them to lose their shape and function. This can have serious consequences as enzymes are involved in vital biochemical reactions in the body.

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  • 45. 

    How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?

    • By acting as a coenzyme for the reaction

    • By binding at the active site of the enzyme

    • By changing the free energy change of the reaction

    • By decreasing the activation energy of the reaction

    • By changing the shape of a reactant

    Correct Answer
    A. By changing the shape of a reactant
    Explanation
    A noncompetitive inhibitor decreases the rate of an enzyme reaction by changing the shape of a reactant. This means that the inhibitor binds to a site on the enzyme that is different from the active site, causing a conformational change in the enzyme. As a result, the enzyme's active site undergoes a change in shape, making it less able to bind to the substrate and catalyze the reaction effectively. This ultimately decreases the rate of the enzyme reaction.

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  • 46. 

    A series of enzymes catalyse the reaction X 􀀏 Y 􀀏 Z 􀀏 A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. What is substance X?

    • A coenzyme

    • A substrate

    • A product

    • An intermediate

    • An allosteric inhibitor

    Correct Answer
    A. A substrate
    Explanation
    In the given scenario, substance X is identified as a substrate. This is because the reaction starts with X and proceeds through a series of reactions (X 􀀏 Y 􀀏 Z 􀀏 A) catalyzed by enzymes. The fact that product A binds to the enzyme that converts X to Y indicates that X is a substrate for this enzyme. This binding of A to the enzyme also decreases its activity, further supporting the notion that X is a substrate in this reaction.

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  • 47. 

    A series of enzymes catalyse the reaction X 􀀏 Y 􀀏 Z 􀀏 A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme. Substance A functions as

    • The substrate

    • A coenzyme

    • A competitive inhibitor

    • An allosteric inhibitor

    • An imtermediate

    Correct Answer
    A. An allosteric inhibitor
    Explanation
    In this scenario, Substance A binds to the enzyme at a site that is not the active site, which is characteristic of an allosteric inhibitor. This binding causes a decrease in the enzyme's activity, suggesting that Substance A is inhibiting the enzyme's function. Therefore, Substance A is functioning as an allosteric inhibitor.

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  • 48. 

    The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as

    • Metabolic inhibition

    • Noncooperative inhibition.

    • Reversible inhibition.

    • Feedback inhibition

    • Allosteric inhibition.

    Correct Answer
    A. Feedback inhibition
    Explanation
    Feedback inhibition is the mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway. This helps regulate the production of the end product and prevent excessive accumulation. When the concentration of the end product reaches a certain level, it binds to an enzyme involved in an earlier step, causing a conformational change that inhibits the enzyme's activity. This negative feedback loop helps maintain homeostasis and ensures that the metabolic pathway is functioning at an optimal level.

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  • 49. 

    Which of the following statements describes enzyme cooperativity?

    • A multi-enzyme complex contains all the enzymes of a metabolic pathway.

    • A product of a pathway serves as a competitive inhibitor of an early enzyme in the pathway.

    • A substrate molecule bound to an active site affects the active site of several subunits.

    • A substrate binds to an active site and inhibits cooperation between enzymes in a pathway.

    • Several substrate molecules can be catalysed by the same enzyme.

    Correct Answer
    A. A substrate molecule bound to an active site affects the active site of several subunits.
    Explanation
    A substrate molecule bound to an active site affects the active site of several subunits. Enzyme cooperativity refers to the phenomenon where the binding of a substrate to one active site of a multi-subunit enzyme complex affects the activity of other active sites within the complex. This can result in a change in the affinity or activity of the other subunits, leading to a coordinated response in the enzymatic activity of the complex. This type of cooperativity is often observed in enzymes involved in metabolic pathways, where the binding of a substrate to one enzyme can enhance or inhibit the activity of other enzymes in the pathway.

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  • Mar 20, 2023
    Quiz Edited by
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  • Jun 05, 2011
    Quiz Created by
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